LTE-Advanced (LTE-A) system improves spectrum efficiency by utilizing a diverse set of base stations deployed in a heterogeneous network topology. Using a mixture of macro, pico, femto and relay base stations, heterogeneous networks enable flexible and low-cost deployments and provide a uniform broadband user experience. In a heterogeneous network, smarter resource coordination among base stations, better base station selection strategies and more advance techniques for efficient interference management can provide substantial gains in throughput and user experience as compared to a conventional homogeneous network.
The technology, coordinated multiple points (CoMP), also known as multi-BS/site MIMO, is used to enhance the performance of cell-edge UEs in LTE-Advanced systems. In LTE Rel-11, various deployment scenarios for CoMP transmission and reception are introduced. Among the different CoMP scenarios, CoMP scenario 4 refers to Single Cell ID CoMP in heterogeneous network with low-power remote radio heads (RRH). In CoMP scenario 4, low-power RRHs are deployed within macrocell coverage provided by macro-eNB. Because cell IDs for macro-eNB and RRHs inside the coverage of macrocell are the same, UEs are not able to reuse frequency resources. As a result, system throughput degrades in CoMP scenario 4 as compared to CoMP scenario 3, where lower power nodes within macrocell coverage have different cell IDs from each other.
In CoMP technology, a point is defined as a set of geographically co-located transmit/receiving antennas (e.g., a macro-eNB or a RRH). In order to enable frequency reuse inside the coverage of macrocell for CoMP scenario 4, UE-specific MIMO precoding is one possible way but it requires accurate channel state information (CSI) for each connection between each point and UE. In order to obtain accurate CSI, the association between points and measurement/feedback is necessary so that UE can utilize the CSI to reuse the frequency resources without interference from/to other points. There are potential issues for point association in CoMP scenario 4. Procedures for point association as well as measurement and feedback required to enable point association are sought.